Nano-electromechanical system (NEMS) device structure and method for forming the same

ABSTRACT

A NEMS device structure and a method for forming the same are provided. The NEMS device structure includes a substrate and an interconnect structure formed over the substrate. The NEMS device structure includes a dielectric layer formed over the interconnect structure and a beam structure formed in and over the dielectric layer. The beam structure includes a fixed portion and a moveable portion, the fixed portion is extended vertically, and the movable portion is extended horizontally. The NEMS device structure includes a cap structure formed over the dielectric layer and the beam structure and a cavity formed between the beam structure and the cap structure.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon. Many integratedcircuits are typically manufactured on a single semiconductor wafer, andindividual dies on the wafer are singulated by sawing between theintegrated circuits along a scribe line. The individual dies aretypically packaged separately, in multi-chip modules, for example, or inother types of packaging.

Nano-electro mechanical system (NEMS) devices have recently beendeveloped. NEMS devices include devices fabricated using semiconductortechnology to form mechanical and electrical features. Examples of theNEMS devices include gears, levers, valves, and hinges. The NEMS devicesare implemented in accelerometers, pressure sensors, microphones,actuators, mirrors, heaters, and/or printer nozzles.

Although existing NEMS device structures and methods of fabricating thesame have generally been adequate for their intended purpose, they havenot been entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1Q show cross-sectional representations of various stages offorming a NEMS device structure, in accordance with some embodiments ofthe disclosure.

FIG. 1J′ shows a top-sectional representation of the fourth conductivelayer, in accordance with some embodiments of the disclosure.

FIGS. 2A-2T show cross-sectional representations of various stages offorming a NEMS device structure, in accordance with some embodiments ofthe disclosure.

FIGS. 3A-3E show cross-sectional representations of various stages offorming a NEMS device structure, in accordance with some embodiments ofthe disclosure.

FIG. 3E′ shows a perspective view of the conductive layers of FIG. 3E,in accordance with some embodiments of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. It should be understood that additionaloperations can be provided before, during, and after the method, andsome of the operations described can be replaced or eliminated for otherembodiments of the method.

Embodiments for a nano-electromechanical system (NEMS) device structureand method for forming the same are provided. The NEMS device structureperforms electrical and mechanical function on the nanoscale. FIGS.1A-1Q show cross-sectional representations of various stages of forminga NEMS device structure 100 a, in accordance with some embodiments ofthe disclosure.

Referring to FIG. 1A, a substrate 102 is provided. The substrate 102 maybe made of silicon or other semiconductor materials. In someembodiments, the substrate 102 is a silicon wafer. Alternatively oradditionally, the substrate 102 may include other elementarysemiconductor materials such as germanium. In some embodiments, thesubstrate 102 is made of a compound semiconductor such as siliconcarbide, gallium arsenic, indium arsenide, or indium phosphide. In someembodiments, the substrate 102 is made of an alloy semiconductor such assilicon germanium, silicon germanium carbide, gallium arsenic phosphide,or gallium indium phosphide. In some embodiments, the substrate 102includes an epitaxial layer. For example, the substrate 102 has anepitaxial layer overlying a bulk semiconductor.

An inter-layer dielectric (ILD) layer 104 is formed over the substrate102. In some embodiments, the ILD layer 104 is made of silicon oxide(SiOx), silicon nitride (SixNy), silicon oxynitride (SiON) or anotherapplicable material.

The device element 105 is formed in the ILD layer 104. The deviceelement 105 include transistors (e.g., metal oxide semiconductor fieldeffect transistors (MOSFET), complementary metal oxide semiconductor(CMOS) transistors, bipolar junction transistors (BJT), high-voltagetransistors, high-frequency transistors, p-channel and/or n channelfield effect transistors (PFETs/NFETs), etc.), diodes, and/or otherapplicable elements. In some embodiments, the device element 105includes a gate dielectric layer 106 and a gate electrode 108, and gatespacers 107 are formed on opposite sidewalls of the gate electrode 108.

In some embodiments, device element 105 is formed in the substrate 102in a front-end-of-line (FEOL) process. Various processes are performedto form device elements 105, such as deposition, etching, implantation,photolithography, annealing, and/or other applicable processes.

The substrate 102 may include various doped regions such as p-type wellsor n-type wells). Doped regions may be doped with p-type dopants, suchas boron or BF₂, and/or n-type dopants, such as phosphorus (P) orarsenic (As). The doped regions may be formed directly on the substrate102, in a P-well structure, in an N-well structure, or in a dual-wellstructure.

The substrate 102 may further include isolation features (not shown),such as shallow trench isolation (STI) features or local oxidation ofsilicon (LOCOS) features. Isolation features may define and isolatevarious device elements.

A first etching stop layer 109 is formed over the ILD layer 104, and afirst dielectric layer 110 is formed over the first etching stop layer109 The first etching stop layer 109 is made of a material having adifferent etch selectivity from the first dielectric layer 110. In someembodiments, the first etching stop layer 109 is made of nitride layer,such as silicon nitride. In some embodiments, the first dielectric layer110 is an inter-metal dielectric (IMD) layer. In some embodiments, thefirst dielectric layer 110 is a single layer or multiple layers. Thefirst dielectric layer 110 is made of silicon oxide (SiOx), siliconnitride (SixNy), silicon oxynitride (SiON), dielectric material(s) withlow dielectric constant (low-k), or combinations thereof. In someembodiments, the first dielectric layer 110 is made of an extreme low-k(ELK) dielectric material with a dielectric constant (k) less than about2.5. In some embodiments, ELK dielectric materials include carbon dopedsilicon oxide, amorphous fluorinated carbon, parylene,bis-benzocyclobutenes (BCB), polytetrafluoroethylene (PTFE) (Teflon), orsilicon oxycarbide polymers (SiOC). In some embodiments, ELK dielectricmaterials include a porous version of an existing dielectric material,such as hydrogen silsesquioxane (HSQ), porous methyl silsesquioxane(MSQ), porous polyarylether (PAE), porous SiLK, or porous silicon oxide(SiO₂). In some embodiments, the first dielectric layer 110 is depositedby a plasma enhanced chemical vapor deposition (PECVD) process or by aspin coating process.

Afterwards, a first conductive layer 112 is formed in the firstdielectric layer 110, as shown in FIG. 1B, in accordance with someembodiments of the disclosure. The conductive layer 112 is electricallyconnected to the device element 105 through various metallic lines andvias in the first dielectric layer 110.

An interconnect structure 114 is constructed by the first dielectriclayer 110 and the first conductive layer 112. The first dielectric layer110 and the first conductive layer 112 are formed in a back-end-of-line(BEOL) process. The first conductive layer 112 is made of copper (Cu),copper alloy, aluminum (Al), aluminum alloy, tungsten (W), tungstenalloy, titanium (Ti), titanium alloy, tantalum (Ta) or tantalum alloy.In some embodiments, the first conductive layer 112 is formed by aplating method, electroless plating, sputtering or chemical vapordeposition (CVD).

The first conductive layer 112 includes a number of portions. In someembodiments, the first conductive layer 112 includes a first portion 112a, a second portion 112 b and a third portion 112 c between the firstportion 112 a and the second portion 112 b.

Afterwards, a second etching stop layer 119 is formed over the firstdielectric layer 110, and a second dielectric layer 120 is formed overthe second etching stop layer 119. In some embodiments, the seconddielectric layer 120 is also an inter-metal dielectric (IMD) layer. Insome embodiments, the first dielectric layer 110 and the seconddielectric layer 120 are made of the same materials.

Afterwards, a trench (or via) 123 is formed in the second dielectriclayer 120 to expose a portion of the first conductive layer 112. Thetrench (or via) 123 is formed by a patterning process. The patterningprocess includes a photolithography process and an etching process.Examples of a photolithography process include soft baking, maskaligning, exposure, post-exposure baking, developing the photoresist,rinsing and drying (e.g., hard baking). The etching process may be a dryetching or a wet etching process.

After the trench 123 (or via) is formed, a second conductive layer 122is formed in the trench (or via) 123, as shown in FIG. 1C, in accordancewith some embodiments of the disclosure. The second conductive layer 122is electrically connected to a portion of the first conductive layer112. In some embodiments, the second conductive layer 122 iselectrically connected to the third portion 112 c of the secondconductive layer 112.

The second conductive layer 122 is made of conductive materials. In someembodiments, the second conductive layer 122 is made of doped silicon(Si), copper (Cu), copper alloy, aluminum (Al), aluminum alloy, tungsten(W), tungsten alloy, titanium (Ti), titanium alloy, tantalum (Ta) ortantalum alloy. In some embodiments, the second conductive layer 114 isformed by a plating method, electroless plating, sputtering or chemicalvapor deposition (CVD).

Afterwards, a first sacrificial layer 130 is formed over the seconddielectric layer 120, as shown in FIG. 1D, in accordance with someembodiments of the disclosure. The first sacrificial layer 130 is madeof insulating material. In some embodiments, the first sacrificial layer130 is made of silicon oxide (SiO₂). In some embodiments, the firstsacrificial layer 130 is formed by a deposition process, such as aplasma enhanced chemical vapor deposition (PECVD) process or by a spincoating process.

Afterwards, a hard mask layer 131 is formed over the first sacrificiallayer 130, as shown in FIG. 1E, in accordance with some embodiments ofthe disclosure. The hard mask layer 131 is then patterned to form apatterned hard mask layer 131. The first sacrificial layer 130 is etchedby using the patterned hard mask layer 131 as a mask. Therefore, anumber of first trenches 133 are formed through the first sacrificiallayer 130 and through the second dielectric layer 120. The firsttrenches 133 stop at the second etching stop layer 119. The number offirst trenches 133 should be greater than two, in order to form twosupporting electrodes (formed later).

Afterwards, the second etching stop layer 119 is etched to form thesecond trenches (or vias) 135, as shown in FIG. 1F, in accordance withsome embodiments of the disclosure. As a result, the first portion 112 aand the second portion 112 b are exposed by the second trenches (orvias) 135.

Afterwards, a third conductive layer 136 is formed in the secondtrenches (or vias) 135 and over the first sacrificial layer 130, asshown in FIG. 1G, in accordance with some embodiments of the disclosure.The third conductive layer 136 is electrically connected to a portion ofthe first conductive layer 112. In some embodiments, the thirdconductive layer 136 is electrically connected the first portion 112 aand the second portion 112 b of the first conductive layer 112. Thethird conductive layer 136 passes through the second dielectric layer120 and the third dielectric layer 130.

In some embodiments, the third conductive layer 136 is made of dopedsilicon (Si), copper (Cu), copper alloy, aluminum (Al), aluminum alloy,tungsten (W), tungsten alloy, titanium (Ti), titanium alloy, tantalum(Ta) or tantalum alloy. In some embodiments, the third conductive layer136 is formed by a plating method, electroless plating, sputtering orchemical vapor deposition (CVD).

Afterwards, a polishing process is performed on the third conductivelayer 136 to remove the excess of the third conductive layer 136. Insome embodiments, the polishing process is a chemical mechanicalpolishing (CMP) process. As a result, a top surface of the thirdconductive layer 136 is leveled with a top surface of the firstsacrificial layer 130.

The third conductive layer 136 includes a first portion 136 a and asecond portion 136 b. The first portion 136 a of the third conductivelayer 136 is electrically connected to the first portion 112 a of thefirst conductive layer 112, and the second portion 136 b of the thirdconductive layer 136 is electrically connected to the second portion 112b of the first conductive layer 112.

Afterwards, a second sacrificial layer 140 is formed over the firstsacrificial layer 130, as shown in FIG. 1H, in accordance with someembodiments of the disclosure. In some embodiments, the secondsacrificial layer 140 and the first sacrificial layer 130 are made ofthe same materials.

Afterwards, the second sacrificial layer 140 is patterned to form arecess 141 in the second sacrificial layer 140, as shown in FIG. 1I, inaccordance with some embodiments of the disclosure. Therefore, a portionof the first sacrificial layer 130 is exposed. A top surface of thefirst portion 136 a of the third conductive layer 136 and a top surfaceof the second portion 136 b of the third conductive layer 136 areexposed.

Afterwards, a fourth conductive layer 142 is formed in the recess 141and over the first sacrificial layer 130, as shown in FIG. 1J, inaccordance with some embodiments of the disclosure. Afterwards, aportion of the fourth conductive layer 142 is removed by a polishingprocess. As a result, a top surface of the fourth conductive layer 142is leveled with a top surface of the second sacrificial layer 140.

The fourth conductive layer 142 is electrically connected to the firstportion 136 a and the second portion 136 b of the third conductive layer136. The first portion 136 a, the second portion 136 b and the fourthconductive layer 142 construct a nano-electromechanical system (NEMS)device structure 100 a. In some embodiments, the first portion 136 a ofthe third conductive layer 136 is configured as a first supportingelectrode, the second portion 136 b is configured as a second supportingelectrode, and the fourth conductive layer 142 is configured as a beamstructure of the NEMS device structure 100 a. In other words, the beamstructure of the NEMS device structure 100 a includes a first end and asecond end, the first end is electrically connected to the firstsupporting electrode, and the second end is electrically connected tothe second supporting electrode.

The fourth conductive layer 142 has a length L₁. In some embodiments,the length L₁ is referred to as the beam length. In some embodiments,the length L₁ is in a range from about 700 nm to about 3100 nm. Theoperation voltage (or pull-in voltage) depends on the length L₁, thewidth of the fourth conductive layer 142 and gap between conductivelayer 142 and conductive layer 122. When the length L₁ is within theabove-mentioned range, the operation voltage may be relatively lower.

FIG. 1J′ shows a top-sectional representation of the fourth conductivelayer 142, in accordance with some embodiments of the disclosure. FIG.1J is a cross-sectional representation of the fourth conductive layer142 along the line AA′ of FIG. 1J′. The rectangular dashed line meansthe shapes of the first portion 136 a and the second portion 136 b ofthe third conductive layer 136 which are below the fourth conductivelayer 142.

As shown in FIG. 1J′, the fourth conductive layer 142 includes a numberof strip structures. Compared with a fourth conductive layer made of onestrip structure, the plurality of the strip structures is configured toreduce the resistance of the NEMS device structure. More specifically,the strip structures are arranged in parallel, and therefore theresistance of the fourth conductive layer 142 is reduced.

A pitch P is formed between two adjacent strip structures of the fourthconductive layer 142. In some embodiments, the pitch P is in a rangefrom about 20 nm to about 42 nm. When the pitch P is withinabove-mentioned range, the resistance of the NEMS device structure maymeet requirements. The pitch is depending on what device to replace tomeet area saving requirements.

The NEMS is forming in BEOL and is intended to replace FEOL devicestructures. This means the area saving is from releasing some FEOLdevices and constructs same functional devices by NEMs in BEOL.

After the fourth conductive layer 142 is formed, a third sacrificiallayer 150 is formed over the second sacrificial layer 140 and the fourthconductive layer 142, as shown in FIG. 1K, in accordance with someembodiments of the disclosure. In some embodiments, the thirdsacrificial layer 150 and the second sacrificial layer 140 are made ofthe same materials.

After the third sacrificial layer 150 is formed, a cap structure 160 isformed over the third sacrificial layer 150, as shown in FIG. 1L, inaccordance with some embodiments of the disclosure. More specifically,the cap structure 160 is formed on the NEMS device structure 100 a forthe formation of an encapsulating shell of the NEMS device structure 100a. In some embodiments, the cap structure 160 is made of, nitride,silicon carbide or a combination thereof. In some embodiments, the capstructure 160 is made of silicon nitride, silicon carbide, or anotherapplicable material.

After the cap structure 160 is formed, a number of release holes 161 areformed in the cap structure 160, as shown in FIG. 1M, in accordance withsome embodiments of the disclosure. In some embodiments, the releaseholes 161 are formed by a patterning process including aphotolithography process and an etching process.

After the release holes 161 are formed, the first sacrificial layer 130,the second sacrificial layer 140 and the third sacrificial layer 150 areremoved, as shown in FIG. 1N, in accordance with some embodiments of thedisclosure. Therefore, a first cavity 164 is formed between the fourthconductive layer 142, the first portion 136 a of the third conductivelayer 136 and the second portion 136 b of the third conductive layer136. In addition, a second cavity 146 is formed between the fourthconductive layer 142 and the cap structure 160. The first cavity 164 andthe second cavity 166 are connected to each other.

The first sacrificial layer 130, the second sacrificial layer 140 andthe third sacrificial layer 150 are removed by an etching process, suchas a wet process or dry process. In some embodiments, the sacrificiallayers 130, 140, 150 are removed by a liquid hydrogen-fluoride (HF)solution or a vapor HF. In some embodiments, the first sacrificial layer130, the second sacrificial layer 140 and the third sacrificial layer150 are made of the same materials, and these layers may be removed inthe same etching process. Therefore, the fabrication operation is easy,and the fabrication time is saved.

After the etching process, the fourth conductive layer 142 becomesmovable and is configured as a beam structure. The first portion 136 aof the third conductive layer 136 and the second portion 136 b of thethird conductive layer 136 are used as an anchor to fix the fourthconductive layer 142. The second conductive layer 122 which is formed onthe third portion 112 c of the first conductive layer 112 is used as asensing electrode. The beam structure (e.g. fourth conductive layer 142)moves up and down when the NEMS device structure 100 a is operated,relative to the sensing electrode (e.g. the second conductive layer 122)that senses the movement of the fourth conductive layer 142. Comparedwith the NEMS device structure with one anchor, the NEMS devicestructure of this embodiment has two anchors on both sides forsupporting the beam structure, and therefore reliability of devicesinvolving relative motion of the beam structure can be enhanced.

As shown in FIG. 1N, a gap H is defined between a top surface of thesecond dielectric layer 120 and a bottom surface of the fourthconductive layer 142. Because the gap height H can vary with BEOLinterconnect pitch scaling (in tens of nm range), the operation voltage(or pull-in voltage which is depends on the gap height) can berelatively lower. In some embodiments, the gap height H is in a rangefrom about 20 nm to about 300 nm. The operation voltage (or pull-involtage) depends on the gap height H. When the gap height H is withinthe above-mentioned range, the operation voltage is relatively lower.

After the NEMS device structure 100 a is released, a thin film layer 168is formed over the NEMS device structure 100 a, as shown in FIG. 1O, inaccordance with some embodiments of the disclosure. The fourthconductive layer 142, the first portion 136 a and the second portion 136b of the third conductive layer 136 are covered by the thin film layer168. In addition, the thin film layer 168 is formed over the secondconductive layer 122.

The thin film layer 168 is applied to improve the reliability of theNEMS device structure 100 a. The thin film layer 168 is made of highhardness materials. In some embodiments, the thin film layer 168 is madeof cobalt (Co), tungsten (W), or titanium oxide (TiO₂) or a combinationthereof. In some other embodiments, no the thin film layer 168 is formedover the NEMS device structure 100 a. In some embodiments, the thin filmlayer 168 is formed by an electro-less process.

Afterwards, a first passivation layer 170 is formed in the release holes161 and over the cap structure 160, as shown in FIG. 1P, in accordancewith some embodiments of the disclosure. More specifically, the firstpassivation layer 170 is conformally formed on the cap structure 160.The first passivation layer 170 is configured to seal the release holes161.

In some embodiments, the first passivation layer 170 is made ofinsulating material, such as silicon oxide or silicon nitride. In someembodiments, the first passivation layer 170 is formed by a depositionprocess, such as chemical vapor deposition, spin-on process or anotherapplicable process.

In some embodiments, an air gap 171 is formed in the release holes 161during the formation of the first passivation layer 170. The air-gap 170is simultaneously based on the process used for passivation layer 170.The formation of the air gap 171 is comparable to the followingprocesses.

After the first passivation layer 170 is formed, a second passivationlayer 180 is formed over the first passivation layer 170, as shown inFIG. 1Q, in accordance with some embodiments of the disclosure. Thesecond passivation layer 180 provides a substantially planar surface. Insome embodiments, the second passivation layer 180 is made of insulatingmaterial, such as silicon oxide or silicon nitride.

The fabrication operations shown in FIGS. 1A-1Q for forming the NEMSdevice structure 100 a are integrated with the interconnect structureflow at the BEOL. Therefore, there are more areas which are locatedbelow the NEMS device structure 100 a for forming the logic devices. Inaddition, the beam structure is divided into a number of stripstructures, and therefore the resistance of the NEMS device structure100 a is reduced due to the parallel connection. Furthermore, the NEMSdevice structure 100 a has zero leakage.

FIGS. 2A-2T show cross-sectional representations of various stages offorming a NEMS device structure 100 b, in accordance with someembodiments of the disclosure. Processes and materials used to form thesemiconductor device structure 100 b may be similar to, or the same as,those used to form the semiconductor device structure 100 a and are notrepeated herein.

Referring to FIG. 2A, the substrate 102 is received. The inter-layerdielectric (ILD) layer 104 is formed over the substrate 102. In someembodiments, a device element (such as element 105 in FIG. 1A) is formedin the ILD layer 104. A first etching stop layer 109 is formed over theILD layer 104. The first dielectric layer 110 is formed over the firstetching stop layer 109. A hard mask layer 202 is formed over the firstdielectric layer 110. A photoresist layer 204 is formed over the hardmask layer 202. The photoresist layer 204 is then patterned to form apatterned photoresist layer 204.

After the photoresist layer 204 is patterned, the hard mask layer 202 ispatterned by using the patterned photoresist layer 204, as shown in FIG.2B, in accordance with some embodiments of the disclosure.

Afterwards, a second photoresist layer 206 is formed and patterned overthe hard mask layer 202, as shown in FIG. 2C, in accordance with someembodiments of the disclosure.

Afterwards, a portion of the first dielectric layer 110 is removed byusing the patterned second photoresist layer 206 as a mask, as shown inFIG. 2D, in accordance with some embodiments of the disclosure.

Afterwards, the patterned second photoresist layer 206 is removed, asshown in FIG. 2E, in accordance with some embodiments of the disclosure.

Afterwards, a portion of the first dielectric layer 110 is removed byusing the patterned hard mask layer 202 as a mask, as shown in FIG. 2F,in accordance with some embodiments of the disclosure. First trenches207 and second trenches 209 are formed in the first dielectric layer110. The depth of the first trenches 207 is greater than that of thesecond trenches 209. A portion of the first etching stop layer 109 isexposed by the first trenches 207.

Afterwards, a first diffusion barrier layer 111 and a first conductivelayer 112 are sequentially formed in the first trenches 207 and thesecond trenches 209, as shown in FIG. 2G in accordance with someembodiments of the disclosure.

In some embodiments, the first diffusion barrier layer 111 is made ofTa, TaN, Ti, TiN, or CoW. In some embodiments, the first diffusionbarrier layer 111 is formed by a physical vapor deposition (PVD) processor an atomic layer deposition (ALD) process. In some embodiments, thefirst conductive layer 112 is made of copper, copper alloy, aluminum,aluminum alloys, or a combination thereof. In some embodiments, thefirst conductive layer 112 is formed by plating.

Afterwards, a polishing process is performed on the first conductivelayer 112, as shown in FIG. 2H, in accordance with some embodiments ofthe disclosure. A first interconnect structure 114 a is constructed bythe first etching stop layer 109, the first dielectric layer 110, thediffusion barrier layer 111 and the first conductive layer 112. Thefirst dielectric layer 110, the diffusion barrier layer 111 and thefirst conductive layer 112 are formed in a back-end-of-line (BEOL)process.

Afterwards, a second etching stop layer 119 is formed over the firstdielectric layer 110, and a second dielectric layer 120 is formed overthe second etching stop layer 119, as shown in FIG. 2I, in accordancewith some embodiments of the disclosure. In some embodiments, the firstdielectric layer 110 and the second dielectric layer 120 are made of thesame materials. In some embodiments, the second etching stop layer 119is made of silicon carbide (SiC), silicon nitride (SixNy), siliconcarbonitride (SiCN), silicon oxycarbide (SiOC), silicon oxycarbonnitride (SiOCN), tetraethoxysilane (TEOS) or another applicablematerial.

A second diffusion barrier layer 121 and the second conductive layer 122are formed in the second dielectric layer 120. A second interconnectstructure 114 b is constructed by the second etching stop layer 119, thesecond dielectric layer 120, the second diffusion barrier layer 121, thesecond conductive layer 122. The second interconnect structure 114 b isformed on the first interconnect structure 114 a.

Afterwards, a third etching stop layer 129 is formed over the seconddielectric layer 120. A third dielectric layer 210 is formed over thethird etching stop layer 129, and a third conductive layer 212 is formedin the third dielectric layer 210 and the third etching stop layer 129.The third conductive layer 212 is electrically connected to the secondconductive layer 122.

Afterwards, a sacrificial layer 214 is formed over the third dielectriclayer 210 and the third conductive layer 212, as shown in FIG. 2J, inaccordance with some embodiments of the disclosure. A third photoresistlayer 216 is formed and patterned over the sacrificial layer 214.

After the third photoresist layer 216 is patterned, a portion of thesacrificial layer 214 and a portion of the third dielectric layer 210are removed to form a third trench 217, as shown in FIG. 2K, inaccordance with some embodiments of the disclosure. As a result, aportion of the third etching stop layer 129 is exposed by the thirdtrench 217.

Afterwards, a fourth photoresist layer 218 is formed and patterned overthe sacrificial layer 214, as shown in FIG. 2L, in accordance with someembodiments of the disclosure. In addition, the fourth photoresist layer218 is filled in the third trench 217.

Afterwards, a portion of the sacrificial layer 214 is removed to form afourth trench 219, as shown in FIG. 2M, in accordance with someembodiments of the disclosure.

Afterwards, the fourth photoresist layer 218 is removed, as shown inFIG. 2N, in accordance with some embodiments of the disclosure. As aresult, the third trench 217 and the fourth trench 219 are obtained. Thedepth of the third trench 217 is greater than that of the fourth trench219.

Afterwards, a fifth photoresist layer 220 is formed over the sacrificiallayer 214, as shown in FIG. 2O, in accordance with some embodiments ofthe disclosure. Next, the fifth photoresist layer 220 is patterned toform a patterned fifth photoresist layer 220.

Afterwards, a portion of the sacrificial layer 214 is removed by usingthe patterned fifth photoresist layer 220 as a mask, as shown in FIG.2P, in accordance with some embodiments of the disclosure. As a result,a fifth trench 221 connected to the third trench 217 and the fourthtrench 219 is obtained.

Afterwards, a conductive material is filled into the third trench 217,the fourth trench 219 and the fifth trench 221 and over the sacrificiallayer 214, as shown in FIG. 2Q, in accordance with some embodiments ofthe disclosure. Afterwards, a polishing process is performed to form theNEMS device structure 100 b. In some embodiments, the polishing processis a chemical mechanical polishing (CMP) process.

The NEMS device structure 100 b includes a beam structure 230 formed inand over the second dielectric layer 210. The beam structure 230includes a fixed portion 232 and a moveable portion 234. The fixedportion 232 is extended vertically and has a T-like shape, and themoveable portion 234 is extended horizontally. The moveable portion 234includes a protruding portion 234 a and a main portion 234 b.

Afterwards, the sacrificial layer 214 is removed, as shown in FIG. 2R,in accordance with some embodiments of the disclosure. The sacrificiallayer 214 is removed by a wet process or a dry process. In someembodiments, the sacrificial layer 214 is removed by a liquidhydrogen-fluoride (HF) solution or a vapor HF.

Afterwards, a cap structure 240 formed over the NEMS device structure110 b, as shown in FIG. 2S, in accordance with some embodiments of thedisclosure. A cavity 242 is formed between the NEMS device structure 110b and the cap structure 240. In some embodiments, the cap structure 240is made of silicon oxide (SiO₂), silicon nitride, silicon carbide, oranother applicable material.

The third conductive layer 212 is used as a sensing electrode and isaligned to the protruding portion 234 a of the moveable portion 234 ofthe beam structure 230. When the NEMS device structure 100 b isoperated, the moveable portion 234 a moves up and down, and the movementof the moveable portion 234 a is detected by the sensing electrode (e.g.the third conductive layer 212).

Afterwards, a connector 250 is formed through the third dielectric layer210 and the third etching stop layer 129, as shown in FIG. 2T, inaccordance with some embodiments of the disclosure. The connector 250 iselectrically connected to the second conductive layer 122.

The fabrication operations shown in FIGS. 2A-2M for forming the NEMSdevice structure 100 b are integrated with the interconnect structureflow at BEOL. Therefore, compared with a comparative embodiment with aNEMS device structure formed at FEOL, the areas below the NEMS devicestructure 100 b may be used for forming other logic devices. Inaddition, the beam structure may be divided into a number of stripstructures, and therefore the resistance of the NEMS device structure100 b may be reduced due to the parallel connection. Furthermore, theNEMS device structure 100 b has zero leakage.

FIGS. 3A-3E show cross-sectional representations of various stages offorming a NEMS device structure 100 c, in accordance with someembodiments of the disclosure. Processes and materials used to formsemiconductor device structure 100 c may be similar to, or the same as,those used to form the semiconductor device structure 100 b and are notrepeated herein.

Referring to FIG. 3A, the substrate 102 is received. The inter-layerdielectric (ILD) layer 104 is formed over the substrate 102. In someembodiments, a device element (such as element 105 in FIG. 1A) is formedin the ILD layer 104. The first etching stop layer 109 is formed overthe ILD layer 104. The first dielectric layer 110 is formed over thefirst etching stop layer 109.

The first diffusion barrier layer 111 and the first conductive layer 112are formed in the first dielectric layer 110. The second etching stoplayer 119 is formed over the first dielectric layer 110. The seconddielectric layer 120 is formed over the second etching stop layer 119.The second diffusion barrier layer 121 and the second conductive layer122 are formed in the second dielectric layer 120. A portion of thesecond conductive layer 122 is electrically connected to a portion ofthe first conductive layer 112. The third etching stop layer 129 isformed over the second dielectric layer 120.

The third dielectric layer 210 is formed over the third etching stoplayer 129. The third diffusion layer 211 and the third conductive layer212 are formed in the third dielectric layer 210. A fourth etching stoplayer 304 is formed over the third dielectric layer 210, and aphotoresist layer 306 is formed and patterned over the third etchingstop layer 304. The interconnect structure includes three layers. Thesecond interconnect structure 114 b is formed over the firstinterconnect structure 114 a, and the third interconnect structure 114 cis formed over the second interconnect structure 114 b.

It should be noted that an insulating layer 302 is formed between thesecond conductive layer 122 and the third conductive layer 212.Therefore, the second conductive layer 122 is insulated from the thirdconductive layer 212 by the insulating layer 302.

Furthermore, the third conductive layer 212 includes at least threeportions. In some embodiments, the third conductive layer 212 includes afirst portion 212 a, a second portion 212 b and a third portion 212 cbetween the first portion 212 a and the second portion 212 b. The firstportion 212 a has an extending portion toward the sidewall of the thirdportion 212 c, and the second portion 212 b has an extending portiontoward the sidewall of the third portion 212 c. The shape of the firstportion 212 a and the shape of the second portion 212 b are symmetricalrelative to the third portion 212 c.

After the photoresist layer 306 is patterned, a portion of the fourthetching stop layer 304 is patterned by using the patterned photoresistlayer 306 as a mask, as shown in FIG. 3B, in accordance with someembodiments of the disclosure. Afterwards, a portion of the thirddielectric layer 210, a portion of the second dielectric layer 120, anda portion of the first dielectric layer 110 are removed to form a deeptrench 311. In addition, a portion of the second etching stop layer 119is removed. The deep trench 311 is formed by several etching operations.The deep trench 311 includes a first deep trench 311 a and a second deeptrench 311 b. The first deep trench 311 a is formed between the firstportion 212 a and the third portion 212 c, and the second deep trench311 b is formed between the second portion 212 b and the third portion212 c of the third conductive layer 212.

It should be noted that several interconnect structures are stackedvertically, and then a portion of the dielectric layers are etched bythe etching process. Because the conductive layers are pre-aligned whenthey are stacked, the deep trench 311 will not pass through theconductive layer. The advantage of the fabrication sequence of thisembodiment is that the deep trench alignment issue is resolved.

The deep trench 311 has a uniform width from top to bottom. The deeptrench 311 has a first width D₁. The first width D₁ is equal to adistance D₂ between two adjacent insulating layers 302.

Afterwards, a portion of the third dielectric layer 210, a portion ofthe second dielectric layer 120, and a portion of the first dielectriclayer 110 are removed to enlarge the width of the deep trench 311, asshown in FIG. 3C, in accordance with some embodiments of the disclosure.As a result, the deep trench 311 is enlarged to form a through hole 313.The through hole 313 includes a first through hole 313 a and a secondthrough hole 313 b. The first through hole 313 a is formed between thefirst portion 212 a and the third portion 212 c, and the second throughhole 313 b is formed between the second portion 212 b and the thirdportion 212 c of the third conductive layer 212.

It should be noted that the through hole 313 has a bottom surface and atop surface, and a top width of the top surface is smaller than a bottomwidth of the bottom surface. More specifically, a third width D₃ is adistance defined between a sidewall of the top portion of the firstportion 212 a and a sidewall of the top portion of the third portion 212c. A fourth width D₄ is a distance defined between a sidewall of thebottom portion of the first portion 212 a and a sidewall of the bottomportion of the third portion 212 c. The fourth width D₄ is greater thanthe third width D₃.

As shown in FIG. 3C, the NEMS device structure 100 c includes the firstportion 212 a, the second portion 212 b and the third portion 212 c. Thefirst portion 212 a is configured as a first supporting electrode, thesecond portion 212 b is configured as a second supporting electrode, andthe third portion 212 c is configured as a beam structure of the NEMSdevice structure 100 c. When the NEMS device structure 100 c isoperated, the third portion 212 c moves right and left, and the movementof the third portion 212 c is detected by the first portion 212 a andthe second portion 212 b.

Afterwards, the cap structure 240 is formed over the NEMS devicestructure 100 c, as shown in FIG. 3D, in accordance with someembodiments of the disclosure. The cavity 242 is formed between the capstructure 240 and the NEMS device structure 100 c.

Afterwards, the connector 250 is formed through the second dielectriclayer 210 and the third etching stop layer 129, as shown in FIG. 3E, inaccordance with some embodiments of the disclosure. The connector 250 iselectrically connected to a portion of the third conductive layer 212.

FIG. 3E′ shows a perspective view of the conductive layers 112 c, 122 cand 212 c of FIG. 3E, in accordance with some embodiments of thedisclosure. As shown in FIG. 3E′, the third portion 112 c of the firstconductive layer 112 at the first interconnect structure 114 a isconnected to the third portion 122 c of the second conductive layer 122at the second interconnect structure 114 b. The third portion 122 c ofthe second conductive layer 122 at the second interconnect structure 114b is isolated to the third portion 212 c of the third conductive layer212. Therefore, the beam length L₂ of the beam structure is the sum ofthe length of the third portion 112 c and the length of third portion122 c. In some embodiments, the beam length L₂ of the beam structure ofthe NEMS device structure 100 c is in a range from about 10 um to about20 um (micrometer). When the beam length L₂ is within theabove-mentioned range, the operation voltage (pull-in voltage) isrelatively lower to meet requirements.

The fabrication operations shown in FIGS. 3A-3E for forming the NEMSdevice structure 100 c are integrated with the interconnect structureflow at BEOL. Therefore, the NEMS device structure is formed at BEOL,and the areas below the NEMS device structure 100 c may be used forforming other logic devices. In addition, the operation voltage (pull-involtage) of the NEMS device structure is relatively lower by adjustingthe length of the beam structure.

Embodiments for a NEMS device structure and method for formation thesame are provided. The NEMS device structures are formed atback-end-of-line (BEOL) process. The fabrication operations for formingthe NEMS device structure are integrated with the interconnect structureflow. In addition, the areas which are adjacent to a transistor andbelow the NEMS device structure may be saved and be used as anotherlogic device. Furthermore, the beam structure of the NEMS devicestructure is divided into several strip structures, and therefore theresistance of the NEMS device structure is reduced.

In some embodiments, a NEMS device structure is provided. The NEMSdevice structure includes an interconnect structure formed over asubstrate, and the interconnect structure includes a first conductivelayer formed in a first dielectric layer, the first conductive layercomprises a first portion, a second portion, and a third portion betweenthe first portion and the second portion. The NEMS device structureincludes a second dielectric layer formed over the interconnectstructure and a first supporting electrode formed in and extended abovethe second dielectric layer. The first supporting electrode iselectrically connected to the first portion of the first conductivelayer. The NEMS device structure also includes a second supportingelectrode formed in and extended above the second dielectric layer, andthe second supporting electrode is electrically connected to the secondportion of the first conductive layer. The NEMS device structure furtherincludes a beam structure formed over the first supporting electrode andthe second supporting electrode, and a first cavity is constructed bythe first supporting electrode, the beam structure and the secondsupporting electrode.

In some embodiments, a NEMS device structure is provided. The NEMSdevice structure includes a substrate and an interconnect structureformed over the substrate. The NEMS device structure includes adielectric layer formed over the interconnect structure and a beamstructure formed in and over the dielectric layer. The beam structureincludes a fixed portion and a moveable portion, the fixed portion isextended vertically, and the movable portion is extended horizontally.The NEMS device structure includes a cap structure formed over thedielectric layer and the beam structure and a cavity formed between thebeam structure and the cap structure.

In some embodiments, a NEMS device structure is provided. The NEMSdevice structure includes a substrate and a first dielectric layerformed over the substrate. The NEMS device structure also includes afirst conductive layer formed in a first dielectric layer, and the firstconductive layer includes a first portion, a second portion, and a thirdportion between the first portion and the second portion. The NEMSdevice structure includes a second dielectric layer formed over thefirst dielectric layer and a first supporting electrode, a secondsupporting electrode and a beam structure formed in the seconddielectric layer. The beam structure is formed between the firstsupporting electrode and the second supporting electrode, and the beamstructure is aligned to the third portion of the first conductive layer.The NEMS device structure includes a first through hole formed betweenthe first supporting electrode and the beam structure and a secondthrough hole formed between the second supporting electrode and the beamstructure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A nano-electromechanical system (NEMS) devicestructure, comprising: an interconnect structure formed over asubstrate, wherein the interconnect structure comprises a firstconductive layer formed in a first dielectric layer, the firstconductive layer comprises a first portion, a second portion, and athird portion between the first portion and the second portion; a seconddielectric layer formed over the interconnect structure; a firstsupporting electrode formed in and extended above the second dielectriclayer, wherein the first supporting electrode is electrically connectedto the first portion of the first conductive layer; a second supportingelectrode formed in and extended above the second dielectric layer,wherein the second supporting electrode is electrically connected to thesecond portion of the first conductive layer; and a plurality ofstrip-shaped beam structures formed over the first supporting electrodeand the second supporting electrode, wherein each of the plurality ofstrip-shaped beam structures extends from the first supporting electrodeto the second supporting electrode, a first cavity is constructed by thefirst supporting electrode, the beam structure and the second supportingelectrode.
 2. The NEMS device structure as claimed in claim 1, furthercomprising: a sensing electrode formed over the third portion of thefirst conductive layer, wherein the sensing electrode is electricallyconnected to the third portion of the first conductive layer, and thesensing electrode is not physically in contact with the first supportingelectrode.
 3. The NEMS device structure as claimed in claim 1, whereineach of the plurality of strip-shaped beam structures comprises a firstend and a second end, the first end is electrically connected to thefirst supporting electrode, and the second end is electrically connectedto the second supporting electrode.
 4. The NEMS device structure asclaimed in claim 1, further comprising: a thin film layer covering theplurality of strip-shaped beam structures, the first supportingelectrode and the second supporting electrode.
 5. The NEMS devicestructure as claimed in claim 4, wherein the thin film layer is made ofcobalt (Co), tungsten (W), or titanium oxide (TiO₂) or titanium nitride(TiN) a combination thereof.
 6. The NEMS device structure as claimed inclaim 1, further comprising: a transistor formed below the interconnectstructure.
 7. The NEMS device structure as claimed in claim 1, furthercomprising: a cap structure formed over the plurality of strip-shapedbeam structures, wherein a second cavity is formed between the capstructure and the plurality of strip-shaped beam structures.
 8. The NEMSdevice structure as claimed in claim 7, wherein the cap structurecomprises a plurality of release holes.
 9. The NEMS device structure asclaimed in claim 8, further comprising: a first passivation layer formedin the release holes; and a plurality of air gaps formed in the firstpassivation layer.
 10. A nano-electromechanical system (NEMS) devicestructure, comprising: a transistor formed on a substrate; a firstconductive layer formed over the transistor, wherein the firstconductive layer comprises a first portion and a second portion; adielectric layer formed over the first conductive layer; a firstsupporting electrode formed in and extended above the dielectric layer,wherein the first supporting electrode is electrically connected to thefirst portion of the first conductive layer; a second supportingelectrode formed in and extended above the dielectric layer, wherein thesecond supporting electrode is electrically connected to the secondportion of the first conductive layer; a beam structure formed over thefirst supporting electrode and the second supporting electrode, whereinthe beam structure comprises a plurality of strip structures, each ofthe plurality of strip structures extends from the first supportingelectrode to the second supporting electrode, a first cavity isconstructed by the first supporting electrode, the beam structure andthe second supporting electrode; and a thin film formed on the firstsupporting electrode, the second supporting electrode and the beamelectrode.
 11. The NEMS device structure as claimed in claim 10, whereinthe thin film is made of cobalt (Co), tungsten (W), or titanium oxide(TiO₂) or titanium nitride (TiN) a combination thereof.
 12. The NEMSdevice structure as claimed in claim 10, further comprising: a capstructure formed over the beam structure, wherein the cap structurecomprises a plurality of release holes, and a second cavity is formedbetween the cap structure and the beam structure, and the second cavitysurrounds the first cavity.
 13. The NEMS device structure as claimed inclaim 12, further comprising: a first passivation layer formed in aportion of the release holes; and a second passivation layer formed onthe first passivation layer.
 14. The NEMS device structure as claimed inclaim 10, wherein the first conductive layer further comprises a thirdportion between the first portion and the second portion, and the thirdportion is below the first cavity.
 15. The NEMS device structure asclaimed in claim 14, further comprising: a sensing electrode formed onthe third portion of the first conductive layer, wherein the sensingelectrode is electrically connected to the third portion of the firstconductive layer, and the sensing electrode is not physically in contactwith the first supporting electrode.
 16. The NEMS device structure asclaimed in claim 15, wherein the thin film covers a top surface of thesensing electrode.
 17. A nano-electromechanical system (NEMS) devicestructure, comprising: a transistor formed on a substrate; a dielectriclayer formed over the transistor; a first supporting electrode formed inand extended above the dielectric layer; a second supporting electrodeformed in and extended above the dielectric layer; a plurality ofstrip-shaped beam structures connecting the first supporting electrodeand the second supporting electrode, wherein each of the plurality ofstrip-shaped beam structures extends from the first supporting electrodeto the second supporting electrode, a first cavity is constructed by thefirst supporting electrode, the beam structure and the second supportingelectrode; and a cap structure formed over the beam structure, wherein asecond cavity is formed between the cap structure and the beam structureand the second cavity surrounds the first cavity.
 18. The NEMS devicestructure as claimed in claim 17, further comprising: a thin film formedon the first supporting electrode, the second supporting electrode andthe beam electrode.
 19. The NEMS device structure as claimed in claim17, wherein the cap structure comprises a plurality of release holes, afirst passivation layer formed in the release holes, and an air gap isformed in the first passivation layer.
 20. The NEMS device structure asclaimed in claim 10, further comprising: a first passivation layerformed in the release holes, and an air gap is in the first passivationlayer.